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Author Topic: 1/4 wave vs 5/8 wave  (Read 1941 times)
KD9FRQ
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Posts: 355




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« on: June 25, 2018, 06:36:56 AM »

I am working some mage mount antenna and APRS.

Is there any reason why ARPS would work better both directions while driving when using a short, stiff, 1/4 wave with "coil" twist near base when compared to a Larson 5/8 wave with an NMO mag mount?

When using the 5/8 , I am sending a lot of packets but not all reach the local receivers. And I never get a successful packet RX.

When using the 1/4 wave, I get a lot more packets reported to APRS.FI and I get a few RX packets.

I even swapped radios (I will be asking about them in a separate post) and get the same results.
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KC0MYW
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Posts: 86




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« Reply #1 on: June 25, 2018, 02:03:53 PM »

How confident are you in the performance of both of these antennas in general? It would be expected to have some variation in performance between two different antennas like that but in your situation I do not believe that it should be extremely drastic if both antennas are functioning properly. Can you do an A/B comparison between the two antennas with another ham using a simplex frequency or maybe even over a local repeater?

I recall a time when I had a 2M Larson 5/8 NMO antenna that did not seem to work well when I first got it. In that case, it was because the little tab inside the housing that screwed onto the mount needed to be bent/pulled out slightly to make better contact with the NMO mount. Once that adjustment was made it worked without a problem for many years and was not removed again until the vehicle was sold. I would suggest perhaps checking yours to see if that may be the case here too.
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KD9FRQ
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Posts: 355




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« Reply #2 on: June 25, 2018, 02:22:15 PM »

Thank you.  I will double check the tab.

I will retest both antennas using FM Voice by trying to reach another Operator.  I know the 1/4 works as I used it a few weeks ago as ground spotter for a local air race.  I can also state the 5/8 wave was working with a local repeater as traveled at lunch today, albeit a little scratchy. The tower is 30 miles from my work site.

BTW, does using a little dielectric grease help?  I did NOT put any on the antenna - just wondering to help make the connection.
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KD9FRQ
Member

Posts: 355




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« Reply #3 on: June 26, 2018, 03:38:48 PM »

Following up........

The 5/8 wave unit works very nicely on FM voice.  I was able to reach a local repeater on the far side of the next county over with it.

The 1/4 wave unit can also hit the repeater from the same location.
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KD9FRQ
Member

Posts: 355




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« Reply #4 on: June 27, 2018, 06:37:04 AM »

Additional followup.......

I switched back tot he 1/4 wave and had every outbound packet registered on APRS.FI this morning - during a pretty intense storm.

I only received 3 successful Inbound packets (all being repeats of mine).  that is three more that 5/8 wave antenna got yesterday.

So what is the reason why 1/4 wave is working better than 5/8 wave for APRS?
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W1VT
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Posts: 3224




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« Reply #5 on: June 28, 2018, 06:10:16 AM »

An SWR analyzer that covers the appropriate frequency range is the modern tool for sorting out antenna issues.  A broken antenna usually has a  high SWR.  Feedline issues are also common with antennas that don't work.  I thought I had an issue with a common mode choke feeding a remote antenna switch, as two antennas went bad.  Turned out that a rodent had chewed on both feedlines!

Zak W1VT
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NK7Z
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Posts: 2485


WWW

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« Reply #6 on: June 28, 2018, 07:53:34 AM »

Wow Zac,
That is quite a coincidence!  You all have some aggressive rodents there!  Smiley  I just finished a check of a friends antenna, all was well, used an AA-600, which makes that process almost instant...
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Thanks,
Dave
Amateur Radio: RFI help, Reviews, Setup information, and more...
https://www.nk7z.net
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